The present invention relates to detection methods and devices for a throttle opening degree related to adjustment of the intake air amount of internal combustion engines, and to compensation methods and devices for a target throttle opening degree.
For internal combustion engines, particularly gasoline engines, a technique for accurately adjusting the throttle opening degree by conducting an electronic control procedure in correspondence with the operational state of an accelerator pedal and that of an engine is known.
The throttle opening degree is detected by a throttle opening degree sensor provided in a throttle valve. The throttle valve is actuated and controlled by an electric motor such that the throttle opening degree reaches a target value set in correspondence with an accelerator pedal position, an operational state or a required combustion state.
However, when a deposit of unburned fuel or lubricant oil is formed in the installation portion of the throttle valve, the relationship between the throttle opening degree and the intake air amount is changed. That is, even if the throttle opening degree is maintained as constant, the intake air amount may be decreased as compared to the initial state. This makes it difficult to accurately operate and control the internal combustion engine.
Conventionally, in order to solve this problem, when the engine is operated in a specific operational state, such as an idle state, the difference between the reference throttle opening degree and the actual throttle opening degree is determined and learned. The learned value is used as a correction value in a throttle opening degree control procedure when the engine is operated in different operational states other than the aforementioned state (see Japanese Laid-Open Patent Publication No. 2000-257490). Further, according to the aforementioned document, the difference between the reference throttle opening degree and the actual value varies among the different engine operational states even if the amount of the deposit is maintained as constant, such that the correction value for such difference has to be changed correspondingly. Therefore, in this technique, the learned value is corrected by a learned value correction coefficient that varies depending on in which operational state the engine is running. The throttle opening degree is thus adjusted by the corrected learned value.
However, if the opening degree of the throttle valve is much larger than that of the idle state, the learned value must be increased by a relatively large margin, in accordance with the correction coefficient. This may decrease the correction accuracy of the difference between the reference throttle opening degree and the actual value. That is, in an engine operational state different from the specific operational state in which learning is performed as aforementioned, it is difficult to control the throttle opening degree with enhanced accuracy.